This invention relates to the field of borehole telemetry. More particularly, this invention relates to the field of rotation sensors for borehole telemetry whereby borehole parameters are sensed and telemetered to the surface only when the drill string has ceased rotation or reached a predetermined low rate of rotation.
In the field of borehole drilling, particularly oil and gas well drilling, the usefulness of a system capable of detecting certain parameters at the bottom of a drill string and transmitting such data to the surface during the course of drilling has long been recognized. Several systems have been proposed for accomplishing sensing and data transmission. One of the principal types of such systems is the mud pulse telemetry system wherein pulses ar generated in the mud column in the drill string for transmission of the data to the surface. The present invention is particularly adapted for use in mud pulse transmission systems.
In the case of several classes of data, it is quite unnecessary to obtain readings more frequently than once every 30 feet or so of depth of the well. This corresponds to readings every 1/4 to 11/2 hours at typical penetration rates of 120 feet per hour to 20 feet per hour. It, therefore, becomes desirable to turn off the downhole parameter sensing equipment during long periods of drilling thereby minimizing wear which would otherwise result from continuous operation of the parameter sensors.